1. Field of the Invention
The present invention relates to an industrial machine having an abnormal vibration detecting function, and more particularly to an industrial machine taking a countermeasure against abnormal vibration exerted on a position detector provided for servo control of a movable part of the industrial machine.
2. Description of the Related Art
In various kinds of machines, vibration is caused with a machining operation by a machining tool such as a cutting tool or with driving of a table. Some vibration of a machine is caused even when the machine is normally operated, and a level of the vibration is usually increased when an abnormality is caused or is going to be caused in a machine. For example, when wear of a tool tip has progressed, destruction such as crack has occurred or is going to occur in a tool tip, or a machining condition is improper (for example; a rotational speed of a spindle is excessively large), abnormal vibration occurs.
Normally, an operator recognizes the abnormal vibration by abnormal sound or the like and takes necessary measure such as stopping a machine, checking it or interchanging a tip. However, it is difficult even for a skilled operator to firmly recognize occurrence of abnormal vibration at an early stage and take appropriate measure and it depends on intuition of an operator.
Further, when there causes a situation in which a vibration level is rapidly increased by destruction such as chipping off of a tool tip, an operator is liable to be delayed in dealing therewith. Particularly, in the case in which there is a cause of occurrence of abnormal vibration in a peripheral portion (for example, motor, reduction gear) of a position detector (typically, pulse coder), if the abnormal vibration is left, adverse influence is effected on the position detector, machining accuracy is deteriorated owing to abnormal operation of the position detector and in an extreme case, destruction of the position detector is resulted. Further, there is a case in which a position detector per se constitutes a source of abnormal vibration and in such a case, there is needed a countermeasure of stopping a machine as early as possible.
As a technology for a countermeasure against abnormal vibration of a machine, there has been known a technology in which machining sound caused in, for example, a machine tool is sensed and destruction of a tool tip is predicted based on the result (refer to Japanese Laid-open Patent Publication No. 212656). However, according to the technology, the prime object is prediction of destruction of a machining tool and is not a countermeasure paying attention to influence of vibration which a position detector undergoes.
Generally, a position detector such as a pulse coder is a sensitive precision device in which deviation or destruction is liable to occur by strong vibration. Further, an abnormality in operation of a position detector by deviation or destruction thereof effects adverse influence directly on machining accuracy of a machine and an abnormal output of signal (feedback signal) may cause malfunction. Even in a system for detecting abnormality of machining sound without particularly taking account of a position detector as in the above-described known technology, influence of vibration on a position detector is indirectly taken into consideration to some degree, but abnormal vibration occurred in a position detector per se or its peripheral portion can not necessarily be detected as abnormality of machining sound and may cause delay of taking the countermeasure.
It is an object of the invention to provide an industrial machine capable of precisely detecting vibration caused in a position detector provided at an axis of a machine and thereby swiftly taking a necessary measure. Further, the invention promotes reliability and safety of the machine controlled by a controller and minimizes economic loss by lowering a probability that the position detector reaches unrepairable destruction.
An industrial machine of the invention comprises a mechanical section driven by a servomotor or a spindle motor, and a control section for controlling the mechanical section. A vibration sensor is provided at the servomotor, a detector for detecting position or speed of the servomotor, or a mechanical portion connected with the servomotor or the spindle motor with respect to at least one axis driven by the servomotor or the spindle motor. Information representing the vibration obtained by a signal detected by the vibration sensor is transmitted to the control section.
The control section comprises determining means for determining whether or not a signal detected by the vibration sensor is an abnormal vibration based on the information included in a signal form the vibration sensor. The control section further comprises dealing means for taking measures against the abnormal vibration when the determining means determines that the abnormal vibration is detected.
Alternatively, the detector comprises determining means for determining whether or not the vibration detected by the vibration sensor is abnormal is provided at the detector for detecting position or speed of the servomotor, and the control section takes measures against an abnormal vibration based on the information included in the determination result by the determination means.
The countermeasure against the abnormal vibration includes typically measures of stopping the machine. Further, it is preferable to include a change of machining condition. With regard to the change of machining condition, a progressive change can be carried out. In that case, by changing the machining condition until abnormal vibration is detected, the countermeasure against the abnormal vibration is carried out.
The vibration sensor can be attached to a position detector for one axis or each of the position detectors for a plurality of axes, and in the case of a machine tool, it is preferable to attach the position detector to an axis for axially moving a tool in view of monitoring an environment of vibration of the position detector particularly liable to be subjected to influence of vibration caused in the vicinity of the tool.
In a typical embodiment, the determining means includes operation of comparing high or low of a detected vibration level with a reference level set to the control section. A result of determination may be derived immediately from the high or low comparison, or an allowable value may be provided in a duration time period or a total time period in which the vibration level exceeds the reference level, and a large or small comparison therewith may be carried out.